Tetraenyl prostaglandins

ABSTRACT

This invention encompasses prostaglandins of the formula ##STR1## wherein R represents hydrogen or lower alkyl having 1 to 6 carbon atoms; R 1  represents hydrogen, vinyl, or lower alkyl having 1 to 4 carbon atoms and the wavy line represents R or S stereochemistry; R 2 , R 3 , and R 4  are hydrogen or lower alkyl having 1 to 4 carbom atoms or R 2  and R 3  together with carbon Y form a cycloalkenyl having 4 to 6 carbon atoms or R 3  and R 4  together with carbons X and Y form a cycloalkenyl having 4 to 6 carbons. Compounds of this invention have potent gastric antisecretory and cytoprotective properties with unexpectedly low diarrheogenic side effects.

This is a continuation of application Ser. No. 06/801,370, filed Nov.25, 1985, now U.S. Pat. No. 4,683,328.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,965,143 generally describes compounds of the formula##STR2## wherein R₁, R₂, R₃, R₄, R₆ and R₇ can be hydrogen or a loweralkyl radical, R₅ can be hydrogen or a lower alkanoyl,tetrahydrofuranyl, tetrahydropyran-2-yl, tri(-lower alkyl)silyl or loweralkyl radical, X is a carbonyl, hydroxymethylene or (lower alkanoyl)oxymethylene radical V is a methylene, hydroxymethylene (lower alkanoyl)oxymethylene, tetrahydrofuranyloxymethylene,tetrahydropyran-2-yloxymethylene or tri-(lower alkyl)silyloxymethyleneradical, Y is an ethylene, cis vinylene or transvinylene group, Z is anethylene, cis vinylene, trans-vinylene or ethynylene radical, the wavylines denote the alternative R, S stereochemical configurations, thedotted line indicates an optional double bond, m is an integer greaterthan 2 and less than 5 and R₈ is an alkyl group containing 3-5 carbonatoms or cycloalkyl group containing 5-7 carbon atoms.

British Pat. No. 1,492,426 describes compounds of the structuralformula. ##STR3## wherein R₁, R₂ and R₃ are hydrogen or an alkyl radicalcontaining from 1 to 7 carbon atoms; R₄ is an alkyl radical containingfrom 1 to 7 carbon atoms; R₅ is hydrogen, an alkyl radical containingfrom 1 to 7 carbon atoms or an alkanoyl radical containing from 1 to 7carbon atoms; R₆ is an alkyl radical containing from 2 to 4 carbon atomsor a cycloalkyl radical containing from 5 to 7 carbon atoms; X iscarbonyl or hydroxymethylene; V is methylene, hydroxymethylene oralkanoyloxymethylene wherein the alkanoyl radical contains from 1 to 7carbon atoms; or when X is carbonyl; V may also be a radical of theformula ##STR4## in which the bond represented by the dotted line in thegeneral formula is present; Y is ethylene or vinylene; Y' is vinylene,ethynylene or the group ##STR5## wheren n is 0 to 1 and R₇ and R₈ arehydrogen or an alkyl radical containing from 1 to 7 carbon atoms; Z isethylene, vinylene or ethynylene; and the wavy lines represent thealternative A or B stereochemical configuration or the epimeric mixture:U.S. Pat. No. 4,499,296 describes the compounds of the formula. ##STR6##wherein R"' represents hydroxymethyl, hydroxyacetyl or --CO₂ R"" whereinR"" represents hydrogen or lower alkyl containing 1 to 6 carbon atoms;R' represents lower alkyl containing 1 to 6 carbon atoms, vinyl orethynyl; R" represents cycloalkyl containing 3 to 5 carbon atoms; andthe wavy line represents optional R,S stereochemistry.

European Patent Application No. 84 1136 76.5 describes prostaglandins ofthe formula I ##STR7## wherein X represents cis or trans --CH═CH--,--CH.tbd.C--, methylene or ethylene; R₁ represents a cycloalkyl group ofthe formula ##STR8## where m is 1 to 3 inclusive

R₂ represents hydrogen or lower alkyl with the proviso that the sum ofthe carbon atoms in X and R₁ is 7 or less.

R' represents lower alkyl containing 1 to 6 carbon atoms, vinyl orethynyl; and R"' is as defined above.

DETAILED DESCRIPTION OF THE INVENTION

This invention encompasses a compound of the formula I ##STR9## whereinR represents hydrogen or lower alkyl having 1 to 6 carbon atoms; R₁represents hydrogen, vinyl, or lower alkyl having 1 to 4 carbon atomsand the wavy line represents R or S stereochemistry; R₂, R₃, and R₄ arehydrogen or lower alkyl having 1 to 4 carbon atoms or R₂ and R₃ togetherwith carbon Y form a cycloalkenyl having 4 to 6 carbon atoms or R₃ or R₄together with carbons X and Y form a cycloalkenyl having 4 to 6 carbons.

By lower alkyl is meant straight or branched chain alkyls such asmethyl, ethyl, propyl, isopropyl, butyl, secondary butyl or tertiarybutyl, pentyl, or hexyl with the indicated limitation of the number ofcarbon atoms.

A preferred embodiment is when R₃ and R₄ together with carbons X and Yform a cyclopentenyl ring. These compounds are preferred because oftheir exceptionally high ED₅₀ for diarrhea to ED₅₀ for antisecretoryactivity ratio.

Compounds of this invention are prepared by the following reactionscheme A ##STR10##

The general reaction is decribed in U.S. Pat. Nos. 4,322,543 and4,271,314. These patents also describe methods of varying R fromhydrogens, methyl, ethyl, isopropyl, butyl and the like. The tetraenylprostaglandins of this invention are prepared according to the methodsdescribed for making the more saturated counterparts.

Regardless of the route of administration selected, the novel compoundsof the invention are formulated into pharmaceutically acceptable dosageforms by conventional methods known to the pharmaceutical art.

The compounds can be administered in such oral unit dosage forms astablets, capsules, pills, powders, or granules. They also may beadministered intraperitoneally, subcutaneously, or intramuscularly,using forms known in the pharmaceutical art. In general, the preferredform of administration is oral. An effective but non-toxic quantity ofthe compound is employed in treatment. The dosage regimen forcytoprotection by the compounds of this invention is selected inaccordance with a variety of factors including the type, age, weight,sex, and medical conditions of the patient, the organ to be protected,the route of administration and the particular compound employed. Anordinarily skilled physician will readily determine and prescribe theeffective amount of the cytoprotective agent required to prevent orarrest the progress of the condition. In so proceeding, the physicancould employ relatively low dosages at first, subsequently increasingthe dose until a maximum response is obtained. Dosages of the compoundsof the invention are ordinarily in the area of 0.01 to 10,000 ug/kg.

The cytoprotective utility of compounds of this invention areillustrated by standard test which show their ability to reduceethanol-induced gastric lesions.

0.5 mg/kg is orally administered to adult 180-220 gram male CharlesRiver rats which have been deprived of food for 24 hours. Thirty minuteslayer 1.0 ml of absolute ethanol is administered intragastrically. Therats are sacrificed sixty minutes after alcohol administration and thegastric mucosae are visually examined for the presence of lesions. Thenumber and severity of lesions are scored. A compound is judged activeif it provides a statistically significant reduction in the numberand/or severity of lesions compared to the control group.

The standard test used to detect gastric antisecretory activity isdescribed as follows.

Adult female beagle dogs weighing 6-11 kg. are prepared with wholestomach simple Thomas-type gastric cannulas.

Following full recovery from the surgical implantation of the gastriccannula, the dogs are trained to stand quietly, though fully conscious,in Pavlov-type dog restraining slings and are accustomed to intravenoushistamine infusion.

Experiments are initiated by depriving dogs of food, but not water, for18 hours. With an initial infusion of 0.15M sodium chloride, at aconstant rate of 6.5 ml/hr, gastric secretions collected in plasticbottles affixed to the cannula, are taken at 15 minute intervals andmeasured for volume to the nearest 0.1 ml. Following a 30-45 minutebasal secretion period, the collection bottles are removed, dosing plugsinserted, and compound administered. A 3.0 ml saline which followsimmediately.

After the end of a 30 minute drug absorption period the stomachs areemptied, collection bottles again attached, and the collections, resumedat 30 minute intervals. Simultaneously, the saline infusion is replacedwith a continuous intravenous infusion of histamine dihydrochloride insaline at 15 μg/kg/hr for four hours. Gastric samples are analysed forpH and titratable acidity determinations.

An analysis of the data for each measured or derived variable comparesobservations recorded following treatment with variables obtained forthe same group of animals receiving histamine stimulation alone. Threeparameters, gastric juice volume (ml/30 min), acid concentration(mEq/L), and total acid output (mEq/30 min) are analyzed individually.The data thus obtained are analyzed using interval-by-interval pairedStudent's t-test or two-way analysis of variance to achieve anindication of potency and duration of action. Percentage inhibition iscalculated using pooled mean values for the four hour treatment period.Duration of activity is defined as the length of time of significantinhibition.

Diarrhea is an undesirable side effect commonly associated withantisecretory and cytoprotective prostaglandins. Diarrheogenic activityis demonstrated by the following standardized test. Groups of six adultmale Charles River rats, weight range 180 to 200 grams, are fasted for24 hours prior to administering the test substance. The prostaglandin tobe tested is adminstered intragastrically in iso-osmotic phosphatebuffer at a volume of 10 ml/kg at doses ranging from 100 to 3000microgram/kg. Control animals receive only the vehicle. The rats areplaced in individual wire mesh cages and the trays lined with brownpaper. Diarrhea is assessed at hourly intervals on an all or none basisfor up to eight hours after administration of the prostaglandin.Diarrhea is defined as any loose or water stool. ED₅₀ values areassessed for each hourly diarrheogenic response.

The Compound of Examples 1 and 2 have the following results:

    ______________________________________                                        Antisecretory                                                                 Activity Meal               Thrapeutic                                        Stimulated      Diarrhea Assay                                                                            Index                                             Pavlov Pouch    Rat (iv)    ED.sub.50 diarrhea/                               ED.sub.50 (meg/kg)                                                                            ED.sub.50 (meg/kg)                                                                        ED.sub.50 antisecretory                           ______________________________________                                        Example 1                                                                             0.02        3200        160,000                                       Example 2                                                                             0.05        3200 (inactive)                                           ______________________________________                                    

The following examples illustrate the present invention and are notintended to limit the invention in spirit or scope. Temperatures are indegrees centrigrade unless otherwise indicated.

EXAMPLE 1 1-Cyclopentene Methanol

Lithium Aluminum Hydride (1.69 parts) were suspended in 100 parts byvolume of anhydrous tetrahydrofuran and the suspension was placed undera nitrogen atmosphere at room temperature.

The suspension was stirred and 5.0 parts of 1-cyclopentene carboxylicacid in 100 parts by volume of anhydrous ether were added over a 30minute period. The reaction mixture was stirred for 1 hour after thecompletion of the addition. A 1N hydrochloric acid solution was addeduntil there was no longer an evolution of gas. The reaction mixture wasextracted with an ether/ethyl acetate mixture, the extracts were washedtwo times with potassium carbonate, two times with water and one timewith saturated NaCl. The ether layer was dried over anhydrous sodiumsulfate, the sodium sulfate removed by filtration, and the ther removedby evaporation at reduced pressure to provide 1-cyclopentene methanol.

1-Cyclopentene Carboxaldehyde

Pyridinium chlorochromate (16.1 parts) was suspended in 200 parts byvolume of methylene chloride and 5 parts of 1-cyclopentene methanol in25 parts by volume of methylene chloride were added dropwise. Thereaction mixture was stirred for one hour and diluted with water andextracted with ether. The other extracts were dried over anhydroussodium sulfate, separated, and the ther removed under reduced pressureto provide 1-cyclopentene carboxaldehyde.

4-(1-Cyclopentene)-3-trans-buten-2-one

2.7 parts of the above aldehyde and 11.1 parts oftriphenylphosphoranylidene-2-propanone in 100 parts by volume of toluenewere refluxed for about 16 hours. The solvent was removed bydistillationat atmospheric pressure. The residue was extracted withhexane several times. The hexane extracts were combined, filtered andevaporated to a small volume. The residue was chromatographed on silicagel with 8% ethyl acetate in hexane as eluent to provide 1.3 parts of alight yellow oil which is 4-(1-cyclopentene)-3-trans-buten-2-one.

To 0.146 parts by volume of magnesium in 25 parts by volume oftetrahydrofuran under argon is added a small amount of propargyl bromideand mercuric chloride to initiate reaction. Once the reaction isstarted, 0.714 parts of propargyl bromide and 0.770 parts of4-(1-cyclopentene)-3-trans-buten-2-one in 50 parts by volume oftetrahydrofuran is added dropwise so as to maintain reflux. Uponcompletion of the reaction, the reaction mixture is cooled to roomtemperature and poured into a mixture of ether and 1N HCl. The aqueouslayer is extracted twice with ether. The ether extracts are combined andwashed 3 times with water and one time with saturated sodium chloridesolution, dried over anhydrous sodium sulfate, filtered, and evaporatedto provide a residual oil. The residual oil is distilled under highvacuum to provide4-methyl-4-hydroxy-6-(1'-cyclopentene)-hex-5E-en-1-yne.

To a solution of 1.1 parts of this material in 10 parts by volume ofdimethylformamide containing 1 part of imidazole is added 0.756 parts oftrimethylsilyl chloride. After 30 minutes of stirring, the reactionmixture is poured into an ether/water mixture, extracted with more etherand the organic layers are combined and washed with water and saturatedsodium chloride solution. The solvent is removed and the residual oil ischromatographed on silica gel with 5% ethyl acetate/hexane to provide4-methyl-4-trimethylsilyloxy-6-(1'-cyclopentene)-5E-en-1-yne. 0.715Parts of this material is reacted with 0.838 parts of tri-n-butyl tinhydride at 20° C. catalyzed with ultraviolet light and a few milligramsof (AIBN) azobisisobutyronitrite to provide a compound of the formula.##STR11##

1.6 parts of this trans vinyl tin product is dissolved in 3 parts byvolume of tetrahydrofuran, cooled to -60° C. and 8.86 parts by volume of1.66 molar n-butyl lithium is added while maintaining the reactionmixture in an argon atmosphere. After 1 hour at -60° C. a solution of0.388 parts of copper pentyne and 0.979 parts of hexamethylphosphoroustriamide in 15 parts by volume of ether are added. After 10 minutes asolution of 0.528 parts of7-(3-triethylsilyloxy-5-oxocyclopent-1-ene)hept-4-cis-enoate (U.S. Pat.No. 4,271,314) in 15 parts by volume of ether are slowly added. Thesolution is stirred for one hour and poured into a mixture of ether and1 N hydrochloric acid. The ether layer is separated, washed twice withwater, filtered, dried over sodium sulfate and the ether is removed byevaporation at reduced pressure. The residual oil is chromatographed onsilica gel (87% ethyl acetate/hexane as eluent) to give the protectedprostaglandin. This material is dissolved in 5 parts by volume of a3:1:1 mixture of acetic acid; tetrahydrofuran; water and is allowed tostand at room temperature for 30 minutes. The solution is diluted withether, washed with water five times, and dried over anhydrous sodiumsulfate. The ether is removed by evaporation at reduced pressure and theresidual oil is chromatographed on silica gel (60% ethyl acetate/hexaneas eluent) to provide methyl7-[3α-hydroxy-2β-(4-hydroxy-4-methyl-6-(1'-cyclopentenyl)-1,5-trans,trans-hexadienyl)-5-oxycyclopentane]-1-α-hept-4-cis-enoatehaving the following formula ##STR12##

The racemic mixture is separated by chromatography on 65% ethylacetate/hexane to provide racemates A and B having the indicatedconfiguration at C-16. ##STR13##

EXAMPLE 2

Following the procedures in Examples 1 and using equivalent quantities:

3-methyl-2-butenol is converted to

3-methyl-2-butene carboxaldehyde which in turn is reacted withtriphenylphosphoranyliden-2-propanane to provide6-methyl-hept-3,5-diene-2-one.

Reaction of this ketone with propargyl magnesium bromide provides4,8-dimethyl-4-hydroxy non-7-ene-1-yne. This alcohol is protected withtrimethylsilyl chloride and converted to trans vinyl tin derivative of4,7-dimethyl-4-trimethylsiloxy-non-8-ene-1-yne which is converted to thecorresponding prostaglandin by the methods described in U.S. Pat. Nos.4,322,543 and 4,271,314 to provide methyl7-[3α-hydroxy-2β-(4-hydroxy-4,8-dimethyl-1,5,7-trans,trans-nonatrienyl-5-oxocyclopentane]-1α-hept-4-cis-enoatehaving the formula ##STR14##

The racemates are separated by chromatography on silica gel using 60%ethyl acetate/hexane as eluent.

What is claimed is:
 1. A compound according to the formula: ##STR15##wherein R represents hydrogen or lower alkyl having 1-6 carbon atoms. 2.A pharmaceutical composition for treating gastric lesions in mammalscomprising a therapeutically effective but non-toxic amount of acompound according to claim 1 as the active agent.
 3. A method oftreating gastric lesions comprising administering to a mammal in need ofsuch treatment a therapeutically effective but non-toxic amount of acompound according to claim 1.